Fix permissions for signing tool

- For some reason, the builder doesn't have permissions to create the
output signature file. Per Kokoro docs, set directories to 777 and files to 666.

Change-Id: Ibbba705dcddaa562382d18261984a90f2f25e982
diff --git a/signing.mk b/signing.mk
index 98f5c0c..9d258fd 100644
--- a/signing.mk
+++ b/signing.mk
@@ -14,6 +14,8 @@
 	         --outdir $(PRODUCT_OUT)/repo/debian_repo \
 	         --confdir $(PRODUCT_OUT)/repo/deb_repo_config \
 	         includedeb stable $(PRODUCT_OUT)/*.deb
+	find $(PRODUCT_OUT)/repo/debian_repo -type d | xargs chmod 777
+	find $(PRODUCT_OUT)/repo/debian_repo -type f | xargs chmod 666
 
 sign-repo: $(PRODUCT_OUT)/repo/debian_repo/dists/stable/Release.gpg
 $(PRODUCT_OUT)/repo/debian_repo/dists/stable/Release.gpg: